The present invention relates to power tongs typically used in the oil and gas industry to make up and break apart threaded joints on pipe, casing and similar tubular members.
Power tongs have been in existence for many years and are generally employed in the oil and gas industry to grip and rotate tubular members, such as drill pipe. It is necessary to grip drill pipe with high compressive forces while applying a high degree of torque in order to break apart or tighten threaded pipe connections. In most cases, power tong designs employ a cam mechanism for converting a portion of the torque into a gripping (compressive) force normal to the pipe. This conversion is often accomplished utilizing a power-driven ring gear having an interior cam surface. A cam follower (roller) on a jaw member rides upon the cam surface. As the ring gear is rotated, the follower (and thus the jaw member) is urged into contact with the pipe. An example of such an arrangement can be seen in U.S. Pat. No. 4,404,876.
Most current power tong designs include a ring gear camming member with an open slot or throat, through which the drill pipe is passed in order to place the power tong in position around the pipe. Some tong designs employ a ring gear camming member which has no open throat and is thus a solid circular member. However, a power tong with a solid ring gear camming member must be employed by passing it over the end of a pipe because there is no open throat to facilitate installation. A power tong with a solid ring gear must be left in place around the pipe until conditions permit removal by sliding the tong off one end of the pipe.
Due to the tremendous forces generated during use, open throat power tongs must resist spreading during use. Prior art open throat tongs employ heavy duty rollers and other support structure to resist spreading. Despite such precautions, prior art tongs often spread and fail during use, resulting in tremendous costs and down time during expensive drilling operations. While power tongs having solid circular camming members do not have the spreading problem, the versatility of open throat designs is much preferred.
Another problem often encountered with power tongs using a rotating cam surface to grip the tubular member is that the axial load on the tubular member is proportional to the torque. Therefore in applications where high torque forces are needed, these types of power tongs may transmit such a high axial load to the tubular member that the tubular member is damaged or rendered unusable.